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OLECULAR UHANGES IRODUCED IN IRON 



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VARIATIONS OF TEMPERATURE. 



Prof. R. H. THURSTON. 




From The Journal of the Franklin Institute. 



PHILADELPHIA 

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135 North Third Street. 

18 7 3. 




Stevens Institute of Technology. 



T4 

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P<g>MK)©£® ©V TMS k&VS g®WJW A. §?SV2KI§. 2§@, 



The second College year commences September 18th, 1872. 



FACULTY. 

HENRY MORTON, Ph. D., President. 

A. M. MAYER, Ph. D., Professor of Physics. 

Late of the Lehigh University, Bethlehem, Pa. 
R. H. THURSTON, C. E., Prof, of Engineering. 

Late of the U. S. Naval Academy, Annapolis, Md. 
Db VOLSON WOOD, 0. E., Professor of Mathematics. 

Late of University of Michigan. 
C. W. McCORD, A. M., Professor of Mechanical Drawing. 
A. R. LEEDS, A. M., Professor of Chemistry. 
C. F. KR(EH, A. M., Professor of Languages. 
Rev. EDWARD WALL, A. M., Professor of Belles Lettres. 

The course of the Stevens Institute is of four years duration, and covers all that 
appertains to the profession of a Mechanical Engineer. By means of Workshops 
provided with excellent machinery, Physical Laboratories whose appointments are 
without an equal, and with the finest Cabinets of Instruments, every opportunity 
for the acquisition of thorough and practical knowledge is afforded. 

REQUIREMENTS FOE ADMISSION. 

Candidates for admission to the first year of the course should not be less than 
16 years of age, and must be prepared to pass a satisfactory examination in arith- 
metic, algebra, (including quadratic equations) geometry as given in Davies r 
Legendre and the six elementary propositions of plane Trigonometry. 

Candidates for admission to the higher classes must be, prepared to pass a satis- 
factory examination in all the studies previously pursued oy the classes which they 
propose to enter. 

Advanced students and men of science desiring to avail themselves of the appli- 
ances of the laboratories of the Stevens Institute, to carry on special investigations, 
may make arrangements to that end with the President. 

For further particulars apply to the President, H. MORTON, Hoboken, N. J. 



ON THE MOLECULAR CHANGES PRODUCED IN IRON 
BY VARIATION OF TEMPERATURE. 

By Prof. R. H. Thurston. 
[From the Journal of the Franklin Institute.] 



1. To determine with accuracy what are the molecular changes 
which are produced in iron by variations of temperature, and of other 
physical conditions, it should*be first ascertained, by experiment and 
observation, what are the normal relations of the molecules, and, 
afterward, by similar means, in what way and to what extent those 
relations may be naturally or artificially altered. 

So much having been done, the investigation of the changes in the 
mechanical properties of iron which result from these molecular 
changes is a secondary research, and should naturally follow the pre- 
ceding, as its sequel. 

The almost insuperable difficulties which are encountered in attempt- 
ing to deal with particles of seemingly infinitessimal dimensions, and 
with intermolecular spaces of immeasurably minute extent, have, as 
yet, prevented a satisfactory prosecution of the first part of the inves- 
tigation by even the ablest physicist, and the second division of the 
subject still remains as a problem only partially solved, notwithstand- 
ing the fact that a considerable amount of experiment and discussion 
has thrown light upon it. 

2. The following may be considered as a statement of the most 
generally accepted views of the molecular constitution of matter—* 
views which are usually considered to most fully accord with observed 
phenomena : 

(1.) All matter consists of indefinitely small parts, having dimen- 
sions and forms which are unchangeable by finite power, and which 
are endued with the properties of impenetrability and inertia. 

(2.) These u atoms " are separated by spaces which are absolutely 
very small, but which are immensely great in comparison with the 
atoms themselves. 

(3.) Several atoms, when united by chemical force, form a mole- 
cule, and aggregations of molecules, with intermolecular spaces, make 
up the masses of all matter. 



(4.) Forces, both of attraction and repulsion, exist between atoms 
and molecules. These forces vary, in intensity, with changes of dis- 
tance between molecules. The resultant of these sets of forces is 
s6metimes attractive and sometimes repulsive, changing at times, and 
under definite conditions, from the one direction to the other. There 
may thus be exhibited several alternations of attraction and repul- 
sion within a very minute range. 

(5.) At sensible and measurable distances the attractive force varies 
inversely as the square of the distance between the centres of attrac- 
tion, and is termed gravitation. 

(6.) Gases manifest repulsion only in a degree which, in " perma- 
nent," or perfect, gases, varies inversely as the volume of the mass. 

Liquids exhibit a perfect equilibrium of attractive and repulsive 
forces, but offer immense resistance to the disturbance of that equi- 
librium, by effort to reduce their volume appreciably, and less, al- 
though still considerable, resistance to its disturbance by increase of 
volume. 

Liquids, however, offer exceedingly slight, and sometimes immeas- 
urably slight, resistance to change of relative position of their parti- 
cles, which, therefore, move more or less freely among each other^ 
according to the greater or less viscosity of the liquid. They thus 
offer little or no resistance to change of form. 

Solids are composed of aggregated molecules existing in the same 
condition of equilibrium as is seen in liquids, and offering similar 
resistance to change of volume, but they differ from liquids in exhib- 
iting resistance to change of form, which resistance can usually only 
be overcome by actual destruction of cohesive force. This peculiar 
condition is the result of that form of force which has been termed 
" polarity." 

(7.) These three forms of matter are not distinctly separated from 
each other, but the same substance may pass, by gradual change, 
from one to another of the several classes, and may, in its ordinary 
state, exhibit such physical characteristics as to make it difficult to 
determine to which of two classes it is to be assigned. 

In addition to the above it may be added : 

(8.) Solid bodies offer a resistance to change of form, which, within 
narrow limits, is proportioned to the magnitude of that distortion. 

Beyond these limits the force producing change of form soon sepa- 
rates the atoms completely, by overcoming gradually the inter-atomic 
forces, and rupture takes place. 



3 

3. The last principle was discovered two centuries ago by that 
wonderfully acute philosopher, Robert Hooke, who published in 1678 
his now well-known law, u ut tensio sic vis." 

The first seven of the preceding principles embody the general 
theory of Roger Joseph Boscovitch, who first published it in an im- 
portant treatise printed in Vienna in 1759. 

Both of these early philosophers based their theories upon such 
unsatisfactory experiments as they were able to observe before scien- 
tific methods had begun to exhibit the exactness and the delicacy now 
characterizing them. 

It seems equally remarkable that their deductions should accord 
so perfectly with later determinations, and that so little progress 
should have been made since, in researches upon inter-molecular 
relations. 

That portion of the theory of Boscovitch which supposes several 
alternations of attractive and repellant resultant forces, has received 
some apparent confirmation by experiment, but it is by no means 
proven. It would seem more probable that the attraction of cohe- 
sion, and the repulsive force of heat energy, are the two simple inter- 
molecular forces which determine intermolecular distances. 

Rankine's theory of molecular vortices affords a hint as to the pos- 
sible action of heat here referred to. 

4. It would seem very possible that phenomena apparently con- 
flicting with this latter belief, will find explanation in molecular 
changes of position, rather than in the interaction of forces differing 
in nature from those familiar to us. 

In all familiar examples of solids the force of repulsion increases 
more rapidly than that of attraction, as the molecules are forced to 
approach each other, and the reverse is observed as they separate. 
The molecules occupy, when undisturbed by external forces, positions 
of equilibrium which have been attained by passing over a range 
through which, at a constant temperature, attractive force has pre- 
dominated, and the alternations referred to above, can, if observed at 
all, only be seen after compressing the mass and forcing the particles 
past this first position of equilibrium. 

The other principles stated, if not absolutely proven by experi- 
ment, are at least rendered extremely probable, and are uncontra- 
dicted by any recorded phenomena. 

Hooke's law has been proven sufficiently exact by numerous ex- 
perimenters upon the tensile and compressible resistances of mate- 



rials, and by Chevandier and Wertheim, and later, more fully, but 
not with more precision, by the writer, in a series of experiments 
upon torsional resistances, in which the apparatus was made self- 
registering.* 

5. We remain at present in almost perfect ignorance of the true 
nature and exact relations of the forces which are concerned in deter- 
mining these physical conditions of matter. 

So much as is known is, apparently, in conflict with every hypoth- 
esis yet proposed, in some essential point, yet we cannot resist the 
conviction that these forces are simple modifications of those most 
familiar to us ; the attractive force being that of cohesion, and the 
repellant force being that of heat motion, while a third force, or 
third component of the one force, is that known as " polarity." 

It would seem, from the experiments of Coulomb, Prof. Henry, 
Plateau and others, that the elasticity and resistance of solids are 
due, principally, to the action of molecular forces during changes of 
molecular grouping, rather than to changes of distances between par- 
ticles. The latter has an exceedingly slight range, but, as shown by 
those experiments of Wertheim, which indicate an alteration of vol- 
ume by tensile stress, an actual, though slight, change of atomic dis- 
tances does probably take place. 

It cannot be asserted that these experiments are absolutely con- 
clusive on this point. 

6. The experiments of Professor Baden Powell upon the effect of 
heat in altering the breadth and diameter of Newton's rings,f are 
strongly confirmatory of the opinion, already expressed, that the re- 
pulsive force of the intermolecular spaces is that of heat motion. 

7. The experiments of Dr. Andrews upon the " critical state " of 
substances passing from the liquid to the gaseous condition, and vice 
versa, are considered, by him, to indicate that those states are " but 
widely separated forms of the same conditions of matter," and that 
the one may be made to pass into the other without abrupt change.J 

M. Cagniard de la Tour made the earliest experiments in this field 
in 1822, and was closely followed by Faraday. 

Dr. Andrews' more recent researches are probably the most com- 
plete and the most fruitful. His investigations of the phenomena 
accompanying the changes of carbonic acid, as to temperature and 
pressure, and, particularly, while passing through that phase of tran- 

* Journal Franklin Institute, April, 1873. 

t Phil. Trans., 1834. J Phil. Trass., 1839. 



sition known as the " critical state," have thrown some light upon 
molecular relations. 

The " critical state" is that condition of matter in which exists, 
when just passing from the liquid to the gaseous state, or the reverse, 
by a regular, as distinguished from the more familiar, irregular pro- 
cess. It constitutes the "debatable ground" between these two 
states of matter, whence it is impossible to determine in which con- 
dition it should properly be considered. 

It is found that, when just approaching this point, liquids are even 
more compressible than in the antecedent gaseous condition. 

Water passes through the critical state at a temperature estimated 
at about 770° Fahr. by M. Cagniard de la Tour, and at a pressure 
too high to be accurately measurable. 

At this high temperature and pressure it dissolved the glass tubes 
in which it was attempted to confine it. 

8. Dr. Andrews found that carbonic acid exhibited this gradual 
and regular change from the gaseous to the liquid condition at a much 
lower temperature. 

The experiments of M. Tresca on the "flow of solidaf"* are ex- 
ceedingly interesting and valuable in this connection, as leading con* 
ifirmation to the views expressed by Dr. Andrews. 

The phenomena of the critical state are considered by high autho- 
rities as strongly confirmatory of that portion of the Boscovitch the- 
ory which most requires confirmation. 

9. After having passed from the gaseous to the liquid state, matter 
is found exceedingly difficult to reduce in volume. A pressure of one 
atmosphere produces, in the case of water, a decrease of volume of 
but forty-six one-millionths.'f 

10. In liquids, attractive force makes itself observable, although 
the extreme mobility of their particles prevents the ready or accurate 
measurement of its value. 

Professor Henry, who made the first attempt to estimate it, con- 
siders that the cohesive force of water is several hundred pounds per 
square inch. This considerable force resists change of distance be- 
tween molecules, but does not perceptibly influence change of form, 
and we have, therefore, the curiours fact to observe, here, of the co- 
existence of high cohesive force with almost perfect mobility of par- 
ticles ; the latter condition rendering the resistance to change of form 
Tery difficult of detection and measurement. 

♦London "Engineering," 1866-67. 

t John Canton, Trans. Royal Soc, 1762, 



6 

11. In the process of transition from the liquid to the solid state, 
in addition to the generally continued diminution of volume, mole- 
cular approximation, and the assumption of new positions of equilib- 
rium by the particles, in consequence of the abstraction of heat, an- 
other, as yet unexplained, action occurs, which may he called, for 
want of a better term, molecular polarization. 

This new force comes into play at a point which is definitely fixed, 
for each substance, on the scale of temperature, and although the 
resistance to forces tending to produce changes of intermolecular 
distances may be but little increased, resistance to change of form 
makes itself observable, generally suddenly, and solidification is pro- 
duced by the fixation of molecules in definite relative positions. 

The characteristic which distinguishes the solid from the liquid 
state is the effect, apparently, of this force of "polarity" simply. 

Dr. Henry remarks, " It is in accordance with the phenomena of 
cohesion to suppose that when a solid is liquefied by increase of tem- 
perature, instead of the attraction of the liquids being neutralized 
by the heat, that the effect of this agent is merely to neutralize the 
polarity of the molecules, so as to give them perfect freedom of mo- 
tion around every imaginable axis." This author was probably the 
earliest to detect, and to state thus precisely, the part played by this 
force of polarity in molecular phenomena. 

12. The cohesive force which makes its appearance when a gas 
becomes liquefied is probably considerably increased in all cases when 
solidification occurs ; but the mobility characteristic of the liquid 
state is so perfect that it is difficult to make the comparison, and we, 
consequently, have scarcely and reliable data from which to estimate 
the value of cohesion in fluids. The most valuable are probable 
those of Prof. Henry,* already referred to, from which he estimated 
the cohesion of water to be nearly that of ice. 

13. In the cases of some, and, probably, of many solids, the rela- 
tion of these intermolecular forces becomes such that, if the force of 
polarity is overcome, and the molecules forced from the relative posi- 
tions which they originally assumed, without, at the same time, chang- 
ing their relative distances to such an extent as to destroy their tena- 
city, they may slide into new positions in which they will tend, under 
the action of this polarity, to remain permanently as before. The 
action here referred to is illustrated by some of Coulomb's experi- 
ments on torsion, by those of the writer on the same point, by M. 

* Proceedings Am. Phil. Soc, 1844. 



Tresca's experiments on the flow of solids, and by the common meth- 
ods of kt squirting " lead pipe and of "spinning" brass. 

In the experiments of Coulomb, a wire which had been twisted so 
far as to have taken a permanent set, was found to have its elasticity 
still unimpaired, and could be twisted as far, without taking a new 
set, as it could originally before taking the first. In some examples, 
several successive positions of set, with equal elastic limits, were 
found. Even a thread of clay, soft and plastic as it is, exhibits this 
peculiar action. The experiments of the writer on iron and steel 
five- eighths of an inch in diameter give precisely similar results. 

These experiments are usually quoted in support of the Bo3covitch 
theory of alternation of attraction and repulsion, but it may cer- 
tainly be questioned whether the view just presented is not by far the 
more probable one — the successive sets being produced by successive 
renewals of the action of polarity, as the molecules were forced to 
move among each other without such increase of intermolecular dis- 
tances as to destroy their cohesion. 

14. In cases of true crystallization we have no means of determin. 
ing whether the formation of the crystal, in its invariable and sym- 
metrical form, is due to Prof. Henry's polarizing force, or to still 
another distinct force, or component of the one intermolecular action. 

Since, however, it would be generally supposed that one force may 
produce both phases of polarization, the universally recognized 
" principle of least action " in nature suggests the belief that there 
is but one. 

The phenomena of magnetism, and of diamagnetism, are undoubt- 
edly exhibitions of molecular action, under these intermolecular forces, 
but it remains to be determined whether they are, also, produced by 
the force under consideration. 

The experiments of MM. Chedeville and Treve, at Brest, and of 
other experimenters, indicate, at least, some relationship between, if 
not the identity of, these forces. i 

15. It is sufficiently evident that, granting the relation of these 
several forces to be such as is indicated by what has preceded, the 
attractive, repulsive and polarizing forces of matter may have any 
relation of intensity, and, consequently, that substances may exist 
in very various conditions. 

We may have a mass of matter, in which repulsion, of any degree 
of intensity, may be recognized only, as with the gases; attraction 
and repulsion may equilibrate each other, uniting to produce a mass 



8 

resisting change of molecular distance, with any degree of force, and 
yet, in the absence of polarity, offering little or no resistance to change 
of form, as is the case with the mobide liquids. The addition of the 
polarizing force confers viscosity upon liquids, and this viscosity has 
every value until, as it becomes great, in proportion to the intensity 
of the other forces, *ve find the mass rigid, and, if cohesion is, at the 
same time, considerable, the body is hard. A body like the diamond 
would have great cohesion, and, relatively, still greater polarity ; 
iron exhibits great cohesion and considerable polarity, at ordinary 
temperatures, polarity vanishing faster than cohesion, probably, when 
the metal is heated. 

16. There are some remarkable, and still mysterious, molecular 
phenomena for which we have neither the space nor the data neces- 
sary to discussion. 

The most striking is what may be termed molecular friction. This 
peculiar phenomenon has been frequently noted, but does not appear 
to have attracted the attention or to have provoked the careful re- 
search that its possible importance should have prompted. 

If a bar of steel is magnetized and demagnetized, it is noticed that 
it most readily accepts afterward the polarity first conferred upon it. 
What is known as ** residual magnetism" is another method, proba- 
bly, of manifestation of the same action. It is well settled that mag- 
netic phenomena are phenomena of, or invariably accompanied by, 
molecular movement, and there appears, in these cases, to be exhib- 
ited a kind of interatomic friction which, producing a "set," prevents 
the return of the particles to their original positions, and allows the 
force of polarity to be most readily overcome in a definite direction. 

The " fatigue," of metals, which has been so fully and elegantly 
investigated by Wohler,* may be an exhibition of the effect of simi- 
lar causes. It may, however, be simply due to unequal tension, and 
the consequent gradual rupture, successively, of overstrained por- 
tions of metal, the work being thus thrown upon smaller and smaller 
sections of sound metal, until the whole becomes finally disrupted. 

The determination of the effects of chemical changes upon mole- 
cular tensions presents a wide and, as yet, almost absolutely un- 
known field of research. 

For one of the most complete and consistent theories of molecular 
physics which has been proposed, we are indebted to Prof. W. A. 
Norton. f 

*Uber die Festtgkeitsversuche mil Eisen und Stahl: A. Wohler, Berlin, 1870. 

t AmericaD Journal of Science and Arts, 1872. % 



9 

17. It will require much additional experimental investigation, and 
far more carefully planned and systematic research than has been 
yet given to the subject, to furnish the basis for a perfectly satisfac- 
tory theory of the nature and modes of action of corpuscular forces. 

If we may draw any conclusions from what is known already, we 
should probably infer that, when in the gaseous condition, the mole- 
cules of matter tend continually to separate, under the action of a 
repellant molecular force, which has greater magnitude as the gas 
is compressed. 

As this compression goes on, either by the application of mechani- 
cal force, or by the abstraction of heat, a point is finally reached at 
which an equilibrium occurs between the forces tending to produce a 
reduction of volume and those tending to expand the mass. 

Any effort which may be made to destroy this equilibrium, and to 
increase the intermolecular distances, and, by the same action, to 
enlarge the volume, may be found, hs in the case of water, to be re- 
sisted with some force, while an effort to produce a change of dis- 
tance, by forcing the particles from their positions of equilibrium in 
the other direction, reducing the volume, may meet very great re- 
sistance. And while resistance to change of distance is observed, it 
may happen that the resistance to change of position, amon.g the 
molecules in a group may be, and often is, quite unobservable. 

18. Abstracting heat still further, solidification finally occurs. 

As, throughout the process of contraction, up to this point, the 
attractive force has gradually increased, in its power of resisting 
disturbance of equilibrium and change of molecular distances, it 
would be anticipated that the solid would exhibit greater cohesion 
than the liquid. There is but little evidence bearing upon this 
point, and it will require extended and skillful, as well as patient, 
investigation, in the field of Prof. Henry's labors, to furnish what 
is needed. What we have learned indicates that this increase does 
occur, and that its amount is very great. 

19. The simple increase of cohesive force, where the distances 
between the molecules are still so immense in comparison with the 
magnitudes of those molecules, would not be expected to give in- 
creased elasticity of volume. On the contrary, during the change 
from the gaseous state the loss of elasticity of volume has been a 
marked characteristic 

(It is considered by some philosophers to be well ascertained that 
the radius of a molecular action is less than one five-millionth of an 



10 

inch in some cases,* and that it probably does not equal one two- 
thousandth of an inch in any instance, f At least one writer con- 
siders that the molecule has an orbital radius not exceeding one two- 
thousand five hundred millionth of an inch. J The existence of ani- 
mal organisms as small as one two hundred and fifty millionth of an 
inch in length indicate that even these figures are not probably too 
small.) 

20. An unavoidable inference from the language of authorities 
most frequently quoted is, that elasticity of form — the quality of 
which the so called elasticity and the resilience of solids is a conse- 
quence — results from the existence of a property in solid matter by 
which change of distance between molecules may occur to a marked 
extent without rupture. 

This, if true, would indicate elasticity of form to vary with elas- 
ticity of volume. 

This, we should infer, may be a mistake, the elasticity of volume 
being probably less in the solid than in the liquid, while elasticity of 
form is absent in the latter. 

If it be the fact that the elasticity of form and the resilience of 
solids are not due to elasticity of volume, primarily, we are justified 
in attributing them to the property of pliability, produced by the 
comparatively wide range of intermolecular movement permitted by 
the force of polarity. In examples of great elasticity it may have 
an intensity, small in comparison with that of the other forces acting 
in the mass, and, at the same time, it, or the cohesive force, or both, 
may vary at a less than ordinary rate with a given change of dis- 
tance. 

21. We have followed what can be considered as scarcely more than 
a train of hypotheses, but it is evident that the faint light which has 
been thrown upon the subject exhibits, at least, a probability that 
they approximate with some degree of closeness to the truth. 

We may deduce from what has been stated, finally, that it is ex- 
tremely probable that the contraction in volume of a solid by approx- 
imation of molecules, will increase the absolute strength while de- 
creasing the viscosity of the body, and, as a consequence, diminish- 
ing the resilience by contracting the elastic limits. The mass might 
have a higher modulus of elasticity, and higher tenacity, but would 
more readily yield under a shock or a blow. 

* Wartman. t Robison. J Gaudin. 



11 

22. We would expect these changes in metals to be most marked 
within ordinary limits of temperature, in the cases of those metals 
which have lowest temperature of solidification, since, in such exam- 
ples, the complete change from absolute mobility to perfect rigidity 
is comprised within the least range of temperature. 

23. All other things being equal, since lowering the temperature 
reduces the mobility of particles, and increases the viscosity of the 
metal, we should anticipate that the greater toughness of the mate- 
rial at the higher temperature, while in the solid state, would not 
only exhibit itself in a greater resilience, but would also modify the 
character of the fracture, when ruptured by external force, making 
it less "short" and glass-like — wherever the substance possessed any- 
thing of the characteristics illustrated by Coulomb's experiments, 
noted above — at a high, than at a low heat. The fracture would be 
expected to appear "fibrous" and '"thready" when, as in ordinary 
wrought iron, foreign substances present or varying quality of metal 
should produce in adjacent parts unequal "drawing down" at the 
higher temperature. 

24. Where, as in iron, the change from the liquid condition through 
the pasty, semi-fluid welding state, to the condition of comparative 
brittleness at ordinary temperatures, has been a somewhat regular 
one, it would be anticipated that the change might continue with still 
further decline in temperature. It would not appear unlikely that 
such change might progress indefinitely, or until resilience was abso- 
lutely destroyed by the approximation of molecules, and the coinci- 
dent fixity due to a maximum intensity of polarity. 

Where the body has sensible viscosity and considerable resilience 
it would be expected that, if broken suddenly, as by a quick jerk, 
its fracture would be complete before the particles, retarded by iner- 
tia and by molecular friction, could have time to shift their positions, 
while, when slowly broken, a considerable amount of motion might 
occur before rupture could be completed. 

In the former case, the appearance of the break and the diminu- 
tion of section would be characteristic of tough, and in the latter, they 
would apparently indicate brittle, material. 

25. Such being, not improbably, a statement of the general effects 
of changes of temperature upon matter, it remains for the engineer 
to determine, by experiment, how fully the most generally useful 
metal, iron, presents an example of these effects, and how far they 
are modified by differences of chemical constitution and of physical 
condition. 



12 

The most interesting and instructive experiments which have yet 
been made are those of Fairbairn, Kirkaldy, Professor Johnson, of a 
committee of the Franklin Institute ; of a committee appointed by 
the King of Sweden, of Brockbank, Joule, Sandberg and Spence. 

26. Tredgold, the celebrated engineer, whose intelligence and ex- 
perience have given his published opinions very great weight, be- 
lieved that any increase of temperature would diminish the tenacity 
of metals. 

Dr. John Percy, on the contrary, with probably the majority of 
engineers, believe the opposite to be the effect, basing the belief upon 
the well-known fact that accidents more frequently occur from frac- 
ture in cold than in warm weather. So common is this belief, that 
the statement recently made, that the real effect of decrease of tem- 
perature, other things being equal, may be to increase tenacity, has 
been received with very general distrust. 

27. The magnitude of a change of tenacity arising from simple ap- 
proximation of molecules, and consequent increase of cohesion, could 
not be expected to be very great, since this change of distance be- 
tween adjacent particles is but about seven one millionths of its ordi- 
nary value for a range of one degree. Were the tenacity to vary as 
the square of the distance, the consequent variation would be but one 
and a half per cent., and would be but two per cent, were it to vary, 
within this range, as the cube of the intermolecular distances for a 
range of one thousand degrees. 

28. In comparing the conclusions deduced by the several experi- 
menters, of whose labors the following is an abstract, some evident 
misconceptions will be noted, which plainly arise from the very com- 
mon error of attempting to estimate the strength of materials from 
experiments in which they are tested by shock, forgetting that a ma- 
terial may be immensely strong, and yet, if brittle, non-resilient, may 
be readily broken by a blow which would leave uninjured a less tena- 
cious, but more ductile, specimen. 

It has evidently been quite unsuspected, by the majority of experi- 
menters, and of writers on this subject, that change of temperature 
may, while producing an alteration of the cohesion of metals, effect a 
directly opposite change in its ductility, and that, consequently, the 
substance may exhibit greater tenacity, and may, therefore, tetter 
resist a steady strain, while at the same time its ductility may be so 
greatly decreased by the same cause as to greatly lessen its resili- 
ence, and thus, though stronger, it may be less capable of resisting 
shocks. 



13 

29. A committee of the Franklin Institute, of the State of Penn- 
sylvania, consisting of Professor W. R. Johnson, Benjamin Reeves, 
and Professor A. D. Bache, were engaged, during a period extending 
from April, 1832, to January, 1837, in experiments upon the tenacity 
of iron and of copper, under the varying conditions of ordinary use. 

The effect of change of temperature upon those metals was inves- 
tigated with equal intelligence and thoroughness, and most valuable 
results were obtained. 

30. Upward of one hundred experiments upon copper, at tempe- 
ratures ranging from the freezing point up to 1000° Fahrenheit, ex- 
hibited plainly the fact that a gradual diminution of strength occurs 
with increase of temperature, and vice versa, and that the change is 
as uniform as the unavoidable irregularities in the structure of the 
method would allow. 

The law of this variation of tenacity, within the limits between 
which the experiments were made, was found to be closely repre- 
sented by the formula, 

D 2 = C T 3 , 

I. e., the squares of the diminutions of tenacity vary as the cubes of 
the observed temperatures measured from the freezing point. 

31. The committee, in the course of their exceedingly judicious 
and complete series of deductions, say:* 

" The temperature of no tenacity is generally supposed to be that 
at which the fusing point of the given substance is placed, and the 
point of maximum tenacity ought upon general principles to be found 
at the point at which least heat prevails, that is, at the natural zero, 
or point of absolute cold, if such a point exists in nature. 

" Between these two extremes, it might be supposed that the tena- 
cities of different substances, particularly such as are capable of pass- 
ing immediately from the solid to the liquid state, would be found to 
obey certain laws. 

"As the total cohesion, at the maximum, would present, to a me- 
chanical agent tending to overcome it, the whole of its resistance, 
and as, at more elevated temperatures, a part of that tenacity would 
be overcome by heat, and the rest would be destroyed by the mechan- 
ical force, it is evidently a question of experiment to decide what 
relation the two forces have to each other at the temperature! between 
the two extremes to which we have just alluded. 

• Report of Committee, p. 74. Philadelphia : Merrihew & Gunn. 1837. 



14 

" To decide the theoretical question, or, in other words, to deduce 
from the experiments a law which might be expressed in an abstract 
form, corresponding to all the possible phenomena, would require a 
state of the materials different from that usually found in commerce 
or employed in the arts. 

" It would also, as we have seen, require a knowledge of that about 
which philosophers, no less than practical men, are far from being 
agreed, namely, the point of absolute cold." 

32. The committee do not fail to observe that there are indications 
that the curve, of which their formula is an approximate equation, 
has, very probably, a point of contrary flexure at a temperature 
somewhat below the highest at which they were able to experiment, 
or near the point at which one-half the tenacity of the material is 
destroyed. 

This inflection of the curve, which indicates that no parabolic for- 
mula can be made to represent, accurately, the change of tenacity 
with varying temperature, is very clearly exhibited in the curve laid 
down from the experiments on the strength of wrought iron, which 
were next made by the committee. 

33. These experiments were 73 in number, at temperatures be- 
tween 212° and 1317° Fahr., and comparisons were made with the 
strength of the same bars at ordinary temperatures, as determined 
by 163 experiments. 

The bars were generally broken at sections reduced by the file, and 
the results give but little indication of the effect of change of tem- 
perature upon the resilience and extensibility of the metal ; but they 
afford most interesting, accurate and valuable measures of the effect 
of heat upon tenacity. 

34. It was this investigation which first disclosed the remarkable 
anomaly of the existence of a point in the scale of temperatures, 
usually, if not invariably, considerably above that of ordinary tem- 
perature, at which the metal exhibits a maximum of tenacity. 

34. By heating a number of bars to 572° F., which was found to 
be very nearly the average temperature of maximum strength, and 
breaking them at that temperature, it was found that a mean of ex- 
periments, on the best qualities of rolled iron, gave this maximum as 
15*17 per cent, higher than the tenacity of the same samples at ordi- 
nary temperatures.' 1 * 

* Report of Committee, p. 213. 



15 

The irregularity of structure of specimens tested was found to cause 
an irregular variation of strength amounting to 10 per cent. 

35. Taking 80° Fahr. as a standard temperature, the committee 
discovered that the fifth power of the diminution of tenacity from the 
maximum, determined as just stated, varied as the thirteenth power 
of the temperature above 80° Fahr.,* or 

D* = C (T — 80°) 13 , 

where D = diminution of tenacity, T = temperature, C = a con- 
stant. 

At the temperature of about 400° and 1200°, points of departure 
from the curve took place as already stated, the deviation from the 
law expressed by the formula becoming quite marked. 

3o. The committee made a series of experiments upon the effect of 
annealing in altering the tenacity of the metal. 

They found no measurable change in specific gravity, except with 
specimens which had been hammer-hardened. The tenacity was 
diminished to an extent which follows very closely the order of tem- 
perature at which annealing was performed, and this loss varied 
from 2J per cent., when annealingVas performed at low temperature, 
to 46 per cent., when the metal was annealed from a bright welding 
heat. 

The result seems quite variable, but, at about 1100°, the losses had 
a mean value of about 15 per cent., while, at a welding heat, they 
averaged nearly 25 per cent. 

In testing old boilerplate, a loss was supposed to have been proven, 
which was attributed to this cause, and which amounted to about six 
per cent. 

Unfortunately, the experiments of the committee do not afford the 
data requisite for determining the resilience of these specimens, and 
we are unable to learn whether the observed depreciation of strength 
was accompanied, as we would expect, by an increase of ductility. 

36. No experiments were made at temperatures less than 32°, and 
it remained for further research to determine the behavior of iron at 
exceptionally low temperatures. The work of the committee was 
most skillfully performed, and most conscientiously recorded and 
reported. Together with the equally exhaustive and thorough work 
of the full committee on steam boiler explosions, of which this was a 
part, it affords most valuable and reliable additions to our experi- 
mental knowledge. 



16 

These were the first experiments ever made on an extended scale, 
and the determination of the area of fractured section, the measure- 
ment of elasticity, of latent heat, specific heat, the conducting power, 
and other properties of iron and copper, were made with much greater 
care than could have been expected at that early period. The com- 
mittee were engaged in the work nearly five years, and the expenses 
incurred were defrayed by the United States Treasury Department. 

37. A somewhat similar series of experiments were made by Sir 
Wm. Fair bairn upon rolled iron,* and the same behavior was noted, 
under varying temperatures, as was so well shown by the earlier re- 
searches of the committee of the Franklin Institute. 

The tenacity of Staffordshire boiler plate was examined at tempe- 
ratures varying from °0 Fahr. to a dull red heat — probably 1000° 
Fahr. 

This iron is not of high quality, and some marked deviations were 
observed from the general direction of alteration of strength. 

The tenacity of the specimens gradually increased, as the tempe- 
ratures rose from 60° to 395° F., and thence diminished, until, at a 
red heat, the strength became reduced to the extent of 25 per cent. 

The tenacity recorded at °0 F. was, however, 6 per cent, greater 
than the mean noted at any other observed higher temperatures, but 
not greater than that of individual specimens. 

38. Other experiments were made upon rivet iron, which was 
necessarily of better quality than the Staffordshire plate. 

The tabular statement of the results shows a gradual and quite 
regular increase of tenacity from 60° to 325° F., the strength being 
given at 68,816 and 84,046 pounds per square inch at those points 
respectively — a difference of 30 per cent. The tenacity then dimin- 
ished as temperature rose, becoming reduced to 35,000 pounds per 
square inch at a red heat. 

The strength at 30° F. was slightly greater than at ordinary tem- 
peratures, the figure given being 63,238 pounds per square inch. 

39. Experiments made by Fairbairn on the effect of temperature 
upon cast iron give less uniform, but still instructive, results. f 

With No. 3 iron very unsatisfactory and contradictory results were 
obtained, in consequence of the irregular character of its structure 
and chemical constitution. 

* British Association Report, 1856. 

t British Association Report, vol. 6, 1837. 



17 

Coed-Talon iron No. 2 exhibited continual decrease of transverse 
strength as the temperatures increased. Both cold and hot blast 
irons were experimented upon, at temperatures ranging from 26° to 
190° Fahr. with the following results : 

Cold blast, at 26° and 190°, decreased in strength in the propor- 
tion of 874 to 743. Hot blast, at 21° and at 190°, decreased in 
strength in the ratio of 811 to 731. 

It should be remarkpd that these experiments were made in the 
early days of hot blast, when the differences in the character of hot 
and cold blast iron were more marked than at a later date, when the 
management of the former had become generally and more perfectly 
understood. 

40. Mr. Fairbairn remarks :* " On the whole, we may infer that 
cast-iron, of average quality, loses strength, when heated beyond a 
mean temperature of 120°, and that it becomes insecure at the freez- 
ing point, or under 32° Fahr." 

He supposed that the fact that, in s >me experiments, he found No. 
3 iron to increase in strength with rising temperature, is due to its 
great "irregularity and rigidity." 

He also remarkaf that " The infusion of heat into a metallic sub- 
stance may render it more ductile and probably less rigid in its na- 
ture, and I apprehend it will be found weaker and less secure under 
the effects of a heavy strain." 

41. The experiments of Roebling, referred to in his report to the 
officers of the Niagara Falls Suspension Bridge Co., in 1860, do not 
throw much light upon the question under consideration. 

Mr. Roebling's remark that metal, of as good quality as that upon 
which he experimented, would be "safe at the North pole," J may 
justify the inference that he supposed that such iron would at least 
not lose tenacity when very cold. 

42. David Kirkaldy, of Glasgow, in December, 1860, while con- 
ducting one of the most extended, accurate and well-arranged experi- 
mental inquiries into the value of the tenacity of iron and steel that 
has yet been made,|| took occasion to examine the action of frost upon 
them. 

* On the Application of Wrought and Cast Iron to Building Purposes : 
London, 1844, p. 66. 

t Journal Franklin Institute, 1840, vol. 25, p. 58. 

t Journal Franklin Institute, 1860, vol. 40 ; p. 361. 

|| Experiments on Wrought-Iron and Steel ; David Kirkaldy, Glasgow, 1863; 
p. 85. 



18 

" A bar of Glasgow B, best J-inch diameter, was converted into 
ten bolts, in the ordinary way. Six were exposed all night to in- 
tense frost, and tested in the morning with the thermometer at 23° 
Fahr. The others were kept in a warm place, and carefully pro- 
tected during testing. Three were tested with gradual, and seven 
with sudden strains." "When the strain was gradually applied, 
there was very little difference between the specimens tested in the 
ordinary condition and the two that were frozen ; the former bore 
55,717 ; the latter, 54,385 ; or 2-1 per cent. less. The difference, 
under sudden strains is somewhat greater, viz., 3*6 per cent, less 
when frozen." This iron was of good quality, and Kirkaldy re- 
marks that " had it been of a coarser description, the difference, 
when frozen, might have been much greater." He concludes! that 
"the breaking strain is reduced when the iron is frozen; with the 
strain gradually applied, the difference between a frozen and an un- 
frozen bolt is lessened as the iron is warmed by the drawing out of 
the specimen." 

Kirkaldy noticed that " The amount of heat developed is consider- 
able when specimen the is suddenly stretched" — an important cir- 
cumstance which had previously escaped the observation of experi- 
menters. 

43. This subject was debated at some length at meetings of the 
Manchester Literary and Scientific Society, some two years ago, 
and experiments were described which afforded data of value and 
interest. 

Mr. William Brockbank described his experiments, made for the 
purpose of determining the effect of cold upon the cohesion of cast- 
iron. Using a mixture of several irons of quite different qualities 
(Cleator red hematite, Pontypool and Blaenavon cold blast and Glen- 
garnock hot blast irons, with scrap added), he found a perceptible 
decrease of strength with decrease of temperature. He noted a 
similar effect where wrought-iron was used. The experience of well- 
known iron-masters was adduced in corroboration of these conclusions, 
the examples being, usually, instances of breakage by shock. The 
conclusion of the experimenter* was that "bar iron, boiler plate, 
wire billets and rails are most materially weakened by the action of 
intense cold, losing their toughness, becoming quite brittle under 

* Experiments on Wrought-iron and Steel ; David Kirkaldy, Glasgow, 1863 ; 
p. 95. 
f Nature, 1871. 



19 

sudden impact, and having their structure changed from fibrous ta 
crystalline." 

44. Sir William Fairbairn stated the results of his experiments, 
substantially as has been already given, attributing the more fre- 
quent breakage of wheel tyres in cold weather, to which allusion had 
been made, to unequal strains due to shrinkage, rather than to loss 
of tenacity. 

45. Dr. Joule gave an account of his own experiments, upon a 
smaller scale, made at temperatures of 12° and 55° Fahr., with 
weights applied without shock. The result indicated an increase of 
strength at the lower temperatures, in the proportion of 58J- to 59f, 
or 2J per cent, as a mean of twelve experiments. Experiments, 41 
in number, in which the breakage was produced by shock, gave the 
opposite result. These experiments were made upon large steel 
needles, and upon cast nails. They have been sometimes ridiculed 
as too insignificant to afford valuable evidence, but, insignificant as 
they may appear, and roughly made as they undoubtedly were, they 
are valuable as giving corroborative evidence of the fact which has 
already been quite proven, that decreasing temperatures, in general, 
produce increased strength, but decreased elongation and resilience. 

He concludes that u Frost does not make either iron (cast or 
wrought) or steel brittle, and accidents arise from the neglect of the 
companies to submit wheels, axles, and all other parts of their rolling 
stock to a practical and sufficient test before using them. 

46. Mr. Peter Spence gave a description of his experiments upon 
bars of cast-iron, one-half inch square, placed on supports nine 
inches apart, and broken by carefully applied and steady pressure. 

Six experiments were made at 60°, and six at 0° Fahr. He sums 
up the evidence thus : 

" The bars at zero broke with more regularity than at 60°, but, 
instead of the results confirming the general impression as to cold 
rendering iron more brittle, they are calculated to substantiate an 
exactly opposite idea, namely, that reduction of temperature cceteris 
paribus, increases the strength of cast-iron." He found this increase 
to amount to 3J per cent, between 60° and 0°. 

47. Subsequently, Mr. Spence made a more extended series of 
experiments. 

He obtained 50 bars of cast-iron (of mixed Scotch brands), each 
three feet long and one-half inch square, cut them into lengths of 
one foot, and mixed them thoroughly. Seventy pieces were tested 



20 

at zero, after 48 hours exposure to a freezing mixture of salt and 
ice, and seventy were tested at 70° Fahr. 

The breaking weights of the pieces averaged 430-3 lbs., warm, and 
442-8 lbs. at zero, the weight being .placed midway between supports 
nine inches apart. 

Mr. Spence finally says :* " I have no hesitation in giving it as an 
ascertained law, that a specimen of cast-iron, having, at 70° Fahr., 
a given power of resistance to transverse strain, will, on its tempera- 
ture being reduced to 0°, have that power increased three per cent." 
Mr. Spence notices a circumstance, which occurred in the course 
of his experiments, which may throw some light upon the molecular 
constitution of metals and thus, indirectly, upon the subject dis- 
cussed. A weight of 449 lbs. had been suspended from one of the 
bars tested, for the space of nearly two minutes ; the bar finally 
broke after a single one lb. weight had been, without the slightest 
jar, lifted off — so slowly, in fact, that its upward motion was barely 
perceptible. It may be imagined that the fact is new evidence of 
the existence of viscosity in even cold iron. 

48. The most complete investigation ever made, particularly to 
determine the effect of changes of temperature in modifying the phy- 
sical properties of iron and steel, was that of Knuff Styffe, the direc- 
tor of the Royal Technological Institute at Stockholm, Sweden, and 
supplemented by the experiments of Christer P. Sandberg, who trans- 
lated the report of Styffe into English. 

The work of the first-named engineer was done at the instance of 
a committee appointed by the King of Sweden. It was commenced 
by Professor Angstrom, continued by Herr R. Thalen, of the Uni- 
versity of Upsala, and by Engineer K. Cronstrand, and it was finally 
concluded, with the assistance of Cronstrand and Lindell, by Styffe, 
who wrote out the results of the whole investigation and made the 
report public. 

These labors were begun in 1863, and extended over several years. 
The conclusions of Styffe were : 

" (1). That the absolute strength of iron and steel is not dimin- 
ished by cold, but that, even at the lowest temperature which ever 
occurs in Sweden, it is at least as great as at ordinary temperature 
(about 60° Fahr)." 

" (2). That, at temperatures between 212° and 392° Fahr., the ab- 

* London Engineering, 1871 ; vol. 11, p. 172. 



21 

solute strength of steel is nearly the same as at ordinary tempera- 
ture, but in soft iron, is always greater." 

" (3). That neither in steel nor in iron is the extensibility less in 
severe cold than at ordinary temperature, but that, from 266° to 
320° Fahr., it is generally diminished, not to any great extent in 
steel, but considerably in iron." 

" (4). That the limit of elasticity, in both steel and iron, lies higher 
in severe cold ; but that at about 284° Fahr., it is lower, at least in 
iron, than at ordinary temperatures." 

" (5). That the modulus of elasticity in both steel and iron is in- 
creased on reduction of temperature, and diminished on elevation of 
temperature; but that these variations never exceed 0-05 per cent, 
for a change of temperature of 1-8° Fahr., and, therefore, that such 
variations, at least for ordinary purposes, are of no special import- 
ance." 

49. An equally well conducted series of experiments on transverse 
strength and the flexure of iron and steel led to the following con- 
clusions: 

"(1). Iron sustains, at lower temperatures, a greater, and at higher, 
a smaller load than at the ordinary temperature, before it obtains 
any perceptible permanent deflections." 

" (2). The modulus of elasticity for steel and iron on flexure, may, 
for practical purposes, and without committing any considerable 
error, be generally assumed equal to that on traction. It is dimin- 
ished by permanent deflection, but may be restored by heating, espe- 
cially if raised to a red heat." 

" (3). By hardening steel, its modulus of elasticity is diminished, 
but this diminution has not, in any of the hardened bars examined, 
amounted to more than about three per cent." 

" (4). The elastic force of iron and steel on flexion, as on traction, 
is increased on reduction of temperature and diminished on elevation 
of temperature. The amount of this increase or decrease for a change 
of temperature equal to 1*8° Fahr. (1° centigrade) does not, how- 
ever, in general, amount to more than 0'03 per cent., and, apparently, 
never rises to 0*05 per cent." 

50. The experimenter states that " the results of the experiments 
given above are evidently opposed to the opinion hitherto commonly 
entertained, viz., that steel and iron become weak or brittle at low 
temperatures," and gives it as his opinion that the cause of the fre- 
quent breakage of rails in cold weather, and of articles made of iron 



22 

and steel, is unequal expansion and contraction and the rigidity of 
supports, where, as is the case with rails, frost may very greatly af- 
fect them. 

51. Sandberg, while admitting the care and the accuracy which 
distinguished this extensive series of experiments, still doubted 
whether the reasons just given were the sole reasons why metals 
should more readily break in cold than in hot weather, and, having 
obtained the consent of the State Railway Administration, he con- 
ducted a series of experiments, in the summer and winter of 1867, at 
Stockholm, to determine whether, with equal rigidity of supports, 
iron rails would yield with equal readiness to blows at the two ex- 
tremes of temperature. 

The rails experimented upon were each cut in two halves, and one 
piece was tested in cold, and the other warm, weather, at tempera- 
tures of 10° and 84° Fahr. respectively. The supports at the ends 
of the rails were granite blocks, placed four feet apart, and resting 
on the smoothly levelled surface of the granite rock. They were 
broken by a heavy drop, weighing nine cwt. 

Sandberg's conclusions, from 20 experiments, are thus given : 

" (1). That, for such iron as is usually employed for rails in the 
three principal rail making countries (Wales, France and Belgium), 
the breaking strain, as tested by sudden blows or shocks, is consider- 
ably influenced by cold ; such iron exhibiting, at 10° Fahr., only 
from one-third to one-fourth of the strength which it possesses at 84° 
Fahr." 

(2). That the ductility and flexibility of such iron is also much af- 
fected by cold ; rails broken at 10° Fahr., showing, on an average 
a permanent deflection of less than one inch, whilst the other halves 
of the same rails, broken at 84° Fahr., showed a set of more than 
four inches before fracture." 

" (3). That, at summer heat, the strength of Aberdare rails was 
20 per cent, greater than that of the Creusot rails ; but that, in 
winter, the latter were 20 per cent, stronger than the former." 

Sandberg suggests that this considerable decrease of toughness at 
low temperatures may be due to the " cold shortness " produced by 
the presence of phosphorus. 

Our knowledge on this point must remain imperfect until similar 
experiments have been made with iron free from phosphorus. 

52. The researches above described constitute the experimental 
basis of our knowledge of the effect of change of temperature in pro- 



23 

ducing alterations of molecular structure and of strength and resili- 
ence in metals. 

A few other less elaborate, though instructive, experiments have 
been made, some of which enlarge our knowledge of molecular phy- 
sics somewhat, although bearing less directly upon the problem under 
consideration. 

53. Professor \V. F. Johnson, in 1844, gave the results of experi- 
ments made under the direction of the United States Navy Depart- 
ment, which revealed the fact that the increased strength, at moder- 
ately high temperatures, which was noted by the committee of the 
Franklin Institute, was retained, on cooling, provided that the bars 
were submitted to powerful tension while heated. 

Prof. Johnson reports* that " the average gain of length of bolts 
of iron treated at the Washington Navy Yard, by this same process, 
was 5*75 per cent., and the gain of strength 16*64, making, together, 
the gain of value 22*4 per cent. 

" In many instances the experiments made at the Franklin Insti- 
tute proved the gain of length to exceed 7 per cent. The report to 
the bureau also confirms what had been previously observed, viz., 
that the total elongation of a bar of iron, broken in its original cold 
state, is from two to three times as great as the same force would 
produce upon it if applied at a temperature of 573°, which force, will, 
moreover, not break the bar at that temperature." 

54. Professor Thompson has indicatedf the existence of a resist- 
ance to molecular movement, such as has been referred to already, 
and designated "molecular friction." He calls it " viscosity." The 
term, thus used, designates a somewhat different property from that 
to which the name is generally applied, and which was illustrated by 
Tresca's experiments, already described, and other similar experi- 
ments. 

He deduced the following : 

(1.) That there is a certain internal resistance which is independ- 
ent of the elastic properties of metals. 

(2.) That it does not affect the co-efficient of elasticity. 

55. A singular action has been recently detected by W. H. John- 
son, X which may prove instructive in this connection. 

* Senate Document, No. 1, 1844—5; and American Journal of Science and 
Arts, 1846, vol. 1, p. 300. 

t Civil Engineers' Journal, Vol. 28. 
J " Iron," April, 1873, p. 452. 



24 

Iron was immersed in hydrochloric acid one or more hours, and 
then tested for elongation and breaking strain. The pieces were 
then heated, and again tested with the following results : 

u (1). That immersion in acid diminishes the breaking strain of 
iron wire from J to 3 per cent., and of steel wire about 4*76 per 
cent. 

"(2). That immersion in acid appears, in some cases, to diminish, 
and, in others, slightly to augment the elongation of iron wire, and 
to augment the elongation of steel wire about 30 per cent." 

Heat restored to the iron its original toughness. 

Pyroligneous and sulphuric acids had the same effect as hydrochlo- 
ric, in different degrees. 

Copper was not affected in this manner. 

The cause of this peculiar action remains undetermined. The phe- 
nomenon is of interest principally as confirming an inference deduci- 
ble from other experiments, viz., that, in general, circumstances 
tending to increase the strength of a metal, by molecular change, 
also tend to reduce its viscosity and its extensibility, and visa versa. 

56. The experiments of Mr. Oliver Williams,* in determining the 
change produced in the character of the fraction of iron by trans- 
verse strain, at extreme temperatures, were more evidently pertinent 
to this subject. 

Mr. Williams says, of two specimens of nut iron, but from differ- 
ent bars, made at Catasauqua, Pennsylvania, " These specimens 
were first nicked with a cleft on one side only, and then broken 
under a hammer, at a temperature of about 20° Fahr. At this tem- 
perature, both specimens broke off short, showing a clearly defined 
granular, or steely iron fracture. The pieces were then gradually 
heated to about 75° Fahr., and then broken, as before, developing a 
fine, clear, fibrous grain. The two fractures were but four inches 
apart, and are entirely different." 

57. It has been long known that a granular fracture may be pro- 
duced by a shock, in iron which appears fibrous when gradually torn 
apart. 

This was fully proven by Kirkaldy.f Mr. Williams was, proba- 
bly, the first to make the experiment just described, and thus to 
make a direct comparison of the characteristics of fracture in the 
same iron at different temperatures. 

* The Iron Age, New York, March 13, 1873, p. 16. 
t Experiments on Iron and Steel. 



25 

A fair inference from these experiments is, apparently, that a re- 
duction of temperature increases the polarizing force, decreases the 
viscosity of the metal, and thus causes its fracture to assume the ap- 
pearance which characterizes the fracture of substances which are 
remarkable for their rigidity ; while elevation of temperature, increas- 
ing viscosity, allows greater extension before fracture, and this greater 
toughness is evidenced by the sort of fracture characteristic of less 
brittle materials. 

58. Nothing in these experiments affords any indication of the 
effect of change of temperature, in this instance, upon the strength 
of the metal. It has, however, been shown that low temperatures 
increase the strength of metals, and Mr. Williams' experiments are 
confirmatory of the supposition, of which strong evidence has already 
been quoted, that it also decreases resilience, or the power of resist- 
ing blows and heavy shocks. 

The experience of every mechanic who has observed the behavior 
of tools and of metals at different temperatures, also confirms this 
belief. Tools yield readily to blows, where exposed to severe cold, 
although not evidently weak under steady strain. 

59. It has been remarked (Article 22), that we should anticipate 
that the effects of change of temperature would be most marked with 
metals of low melting points. 

The observations of Prof. Fritzsche, who noticed that extreme cold 
produced upon tin an effect somewhat similar, but even more striking 
than that remarked by Mr. Williams in the case of iron, may be ac- 
cepted as corroborating this idea. 

The well known variations in the ductility of zinc, when under 
varying conditions of temperature, are also noticeable evidence of 
marked rapidity of such changes, where the range of temperature^ 
within which the body remains solid, is narrow. 

60. Reviewing the whole ground, it becomes evident that there 
still remains much interesting work to be done in determining the 
precise effects of variation of temperature upon the strength and duc- 
tility of the various metals, and, particularly, in ascertaining the 
modifications of the general law, which may be due to differences in 
physical and chemical structure, where they are combined with the 
metalloids, or united as alloys. 

Some of those effects which have been attributed to changes of 
tenacity in the material may have been due, in some degree, to un- 
equal expansion or contraction. It can hardly be doubted that such 



26 

action often modifies, or even disguises, the change in character pro- 
duced by real changes of intermolecular forces. It is certainly the 
fact that changes of molecular arrangement sometimes occur very 
slowly. 

Ordnance of cast-iron has been found to gain strength slowly, but 
probably steadily, for years after its removal from the foundry ; the 
familiar belief that razors, out of use, recover the cutting quality lost 
by constant employment, may be probably founded on fact, and the 
writer has often noticed that cold chisels and similar tools, when 
found after long disuse and exposure to the weather, seem to have 
regained the strength and endurance of edge, the loss of which had 
probably caused the workmen to throw them aside. 

If this be the case, a sudden alteration of structure, such as may 
be produced by considerable changes of temperature, may cause a 
change of quality, which only a long period of time may counteract. 
Such action would evidently be most marked with brittle, and least 
noticeable with ductile, metals, and the fact is further illustrated by 
the circumstance that iron castings, not infrequently, are broken 
while cooling after removal from the mold, while bronze castings are 
very rarely thus injured. 

61. It seems, finally, very probable that additional investigation 
will be found to confirm our deductions from experiments already 
made, and will justify the following 

conclusions : 

1. That the number and the nature of those molecular forces which 
determine the physical condition of matter are not yet fully ascer- 
tained, but that these forces manifest themselves in, at least, three 
distinct modes of action, and, as thus exhibited, they are known as 
repulsion, cohesion and polarity. 

2. That the force of repulsion, is, apparently, heat-motion, or some 
closely related phase of energy ; that the force of cohesion bears 
some resemblance to that of gravitation, but seems not to be identi- 
cal with the latter, and that the force of molecular polarity, which 
determines the molecular relations of position, seems to bear some 
distant resemblance to that of magnetic polarity. 

3. That the law which governs the variations in intensity of these 
forces with changes of intermolecular distances, is undetermined, and 
that it has not been expressed by any mathematical formula, except 
approximately and for a limited range. 



27 

4. That the magnitudes of the intermolecular spaces, and, conse- 
sequently, the volume of any mass, are variable with changes in the 
relative magnitude, of the forces of cohesion and repulsion. 

6. That the resistance offered to change of form is determined by 
the relations, in intensity, of the forces of polarity, and of those 
forces which determine intermolecular distances. 

6. That, at the " absolute zero" ( — 461-2° Fahr.), cohesion and, 
consequently, the strength of the material, have their maximum value, 
heat-energy having disappeared. 

7. That at very high temperatures, heat-energy exerts a separat- 
ing force between particles, which entirely overcomes the other forces, 
and matter assuming the gaseous state requires the action of extrane- 
ous force to preserve its volume unchanged. 

8. That, at intermediate points, matter in either the solid or the 
liquid state exhibits a definite degree of separation of molecules, 
which is determined by the intensity of the repulsion due to heat- 
motion, a position of equilibrium being assumed which, with the 
same substance, is invariable for the same temperature. The appli- 
cation of some kind of force is required to disturb this equilibrium 
and to produce this change of volume. The amount of this force is 
determined, for any given extent of disturbance, by the maximum 
value of cohesion for the substance and the quantity of heat which 
has been required to raise it from the absolute zero of temperature. 
The sum of the applied force, and of the force consequent upon the 
presence of heat-motion, must exceed cohesive force to produce dila- 
tation, while this cohesive force, added to the externally applied 
force, must exceed the force of repulsion to produce diminution of 
volume. 

9. That the distinction between the solid and liquid states of mat- 
ter is due to the action, in the former, of the force of polarity, which 
gives stability of form, while in the latter this force is extremely 
feeble, and disappears altogether before the boundary line between 
the liquid and gaseous states is reached. 

That combined stability and elasticity of volume may be produced 
by the equilibrium of attractive and repulsive forces, but that stabil- 
ity and elasticity of form demand the coexistence of cohesion and 
polarity. 

10. That the general effect of increase or decrease of temperature 
is, in solid bodies, to decrease or increase their power of resistance 
to rupture, or to change of form, and their capability of sustaining 
" dead" loads. 



28 

11. That the general effect of change of temperature i8 to produce 
change of ductility, and, consequently, change of resilience and 
power of resisting shocks and of carrying "live" loads. This change 
is opposite in direction and, usually, in greater degree, than the vari- 
ation simultaneously occurring in tenacity. 

12. That marked exceptions to this general law have been noted, 
but that it seems invariably the fact that wherever an exception is 
observed in the effect upon tenacity, an exception also may be de- 
tected in the effect upon resilience. Those causes which produce in- 
crease of strength appear always to cause a simultaneous decrease of 
ductility, and vice versa. 

13. That experiments upon copper, so far as they have been car- 
ried, indicate that, with that metal, the general law holds good. 

14. That iron exhibits marked deviations from the law, between 
ordinary temperatures and a point somewhere between 500° and 600° 
Fahr., the strength increasing between these limits to the extent of 
about 15 per cent., with good iron. That this variation becomes 
more marked and the observed effects are more irregular as the metal 
is more impure. 

15. That above 600°, and at temperatures below 70° Fahr., the 
general law holds good with iron, its tenacity increasing with dimin- 
ishing temperature below the latter point, at the rate of from about 
0-02 per cent, to 0-03 per cent., for each degree Fahrenheit, while its 
resilience decreases in a much higher but not well determined ratio 
for good iron, and to the extent of reduction to one-third its ordinary 
value or less, at 10° Fahr., when " cold short," and, in the latter 
case, the set before fracture may be less than one-fourth that noted 
at a temperature of 84° Fahr. 

16. That the viscosity, ductility and resilience of metals are deter- 
mined by identical conditions, and that the fracture of iron at low 
temperatures has, accordingly, been found to be characteristic of a 
brittle material, while, at higher temperatures, it exhibits the appear- 
ance peculiar to ductile and somewhat viscous substances. The metal 
breaks, in the first case, with slight permanent set and a short, granu- 
lar fracture, and in the latter with, frequently, a considerable set 
and the form of fracture indicating great ductility. The variation 
in the behavior of iron, as it approaches the welding heat, illustrates 
the latter condition in the most complete manner. 

17. That the precise action of the elements with which iron is 
liable to be contaminated, and the extent to which they modify its 



29 

behavior under varying temperatures, remain to be fully investigated, 
but that the presence of phosphorus, and of other substances produc- 
ing " cold shortness," exaggerates to a great degree the effects of 
low temperature in causing loss of toughness and resilience. 

18. That the modifications of the general law with other metals 
than iron and copper, and in the case of alloys, have not been stu- 
died, and are entirely unknown. 

19. That these conclusions are sustained by experiments of both 
physicists and engineers. 

The practical result of the whole investigation is that iron and 
copper, and probably other metals, do not lose their power of sus- 
taining " dead" loads at low temperatures, but that they do lose, to 
a very serious extent, their power of sustaining shocks or resisting 
sharp blows, and that the factor of safety in structures need not be 
increased in the former case, where exposure to severe cold is appre- 
hended, but that machinery, rails and other constructions which are 
to resist shocks, should have large factors of safety, and should be 
most carefully protected, if possible, from extremes of temperature. 

It will be noticed that nothing in the evidence here quoted indi- 
cates crystallization or any change of molecular grouping to be con- 
sequent upon simple change of temperature.* 

Stevens' Institute of Technology, Hoboken, N. </., May, 1873. 

* It is intended to consider this subject in a succeeding paper. 



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